Oh so the reason people are saying the game is player choice is because the original is also considered player choice.
Generally, the debate has been that it's not, just from different sides. From my perspective, I hold that if you stop playing the game at Disk 1, you would think it's Aerith.
But if you start playing the game at Disk 2, you would just think it's Tifa. Aerith has no presence as a romantic interest from Disk 2 on. Having high affinity with Aerith doesn't lead to alternative version of any scene that preserves Cloud's affections for her. The variations are just the degree of intimacy you have with Tifa.
Put another way, if you watch A New Hope, maybe you think both Luke and Han are love interests to Leia, possibly favoring Luke a bit. If you start from Empire Strikes Back, you think it's Han, but Luke is his love rival. And if you watch Return of the Jedi first, you'll only think of Han (and go "wtf?" about Luke lol).
Different points of the narrative transform the relationship, but once that transformation happens, you don't sustain the earlier developments as if they still apply.